1. Field of the Invention
This invention relates to a suspension controller for improving riding comfort when a vehicle is running on a rough road.
2. Description of the Prior Art
By altering suspension characteristics or a vehicle height in accordance with the condition of a road surface or the attitude of a running vehicle, various suspension controllers for improving riding comfort, controllability and stability of the vehicle have thus far been developed. For example, a suspension controller has been proposed in Japanese Published Unexamined Patent Application No. Sho 59-23712. In such application, the spring constant of an air suspension member and the damping force of a shock absorber are described as being altered by detecting the condition of a road surface on the basis of the acceleration of body movement. According to such prior art, the change in the vehicle height corresponding to the vertical movement of the vehicle is detected, and the spring constant of a suspension system, the damping force of a shock absorber, the stiffness of a joint rubber or the vehicle height is altered when the above-mentioned change in value is greater than a predetermined reference value.
Such prior art, however, have the following problems.
(1) In case a set average height of a vehicle is not in the standard position (NORMAL) but instead is in a high position (HIGH) for driving on a continuous rough road or in a low position (LOW) for high speed driving, the air suspension has been previously set in an expanded or a compressed condition. Consequently, when a vehicle passes over a bump or a dip of a same height, the suspension is apt to be fully compressed or a fully expanded in comparison with a case the vehicle height has been set in a standard position (NORMAL). Under these conditions, bumping between a bound stopper and the body or bumping between a rebound stopper and its seat occurs, which deteriorates riding comfort and increases noise. PA1 (2) In order to cope with the above-mentioned problem, means have been provided for damping the vibration of the body by setting the reference value at a small value and altering the suspension characteristic before a big change in vehicle height is detected. In this case, however, the suspension characteristic is frequently altered corresponding even to a small change in the vehicle height when the predetermined average height is set in the standard (NORMAL) position, whereby riding comfort, controllablity and stability are deteriorated. Moreover, durability and reliability of suspension characteristic alteration actuators also become worse as the frequency of alteration increases. PA1 a vehicle height detection means M1 for detecting a vehicle height at a front wheel and for generating a vehicle height signal according to the distance; PA1 conversion means M3 for converting the vehicle height signal into a corresponding converted height signal, wherein the converted height signal increases more sharply than the vehicle height signal when the vehicle height signal is greater than a preset value and decreases sharply when the vehicle height signal is less than another preset value; PA1 control means M4 for generating a suspension characteristic alteration signal depending on the converted height signal; and PA1 suspension characteristic alteration means M2 for altering characteristics of suspensioning of the vehicle in response to the suspension characteristic alteration signal.